A process for depositing a thin film on a substrate is exemplified by an MOCVD (Metal Organic Chemical Vapor Deposition) method which causes a compound semiconductor crystal to grow. The MOCVD method is used in production of a light emitting diode, a semiconductor laser, a space solar power device, and a high-speed device.
According to the MOCVD method, a substrate is mounted on a mounting table first, and the substrate is heated by use of a heater. Subsequently, as source gasses contributing to deposition, an organic metallic gas such as trimethyl gallium (TMG) and a hydride gas such as ammonia (NH3) are injected onto the substrate, so as to cause a vapor phase reaction. Then, a compound semiconductor crystal is deposited on the substrate. In such a deposition process, it is necessary to cause a temperature of the substrate to be uniform so as to secure high in-plane uniformity. Alternatively, it is necessary to set an appropriate temperature distribution pattern suitable for a deposition device. Therefore, zone control which causes a plurality of heaters to carry out temperature control is known as a method for subjecting a substrate to temperature control (see Patent Literature 1, for example).
FIG. 7 is a block diagram showing an arrangement of a zone control system which causes a plurality of heaters to carry out temperature control as described above. Note that FIG. 7 shows a case of zone control which uses three heaters that are a main heater M and two sub heaters S1 and S2.
A conventional heating control system includes a control device 101 such as a sequencer which serves a host device, temperature control means 102, a distributor 103, a heater power source 104M which is a power source of the main heater M, heater power sources 104S1 and 104S2 which are power sources of the respective sub heaters S1 and S2, and a thermocouple (TC) 105 (see FIG. 7).
According to the conventional heating control system, the control device 101 sets a target temperature SPm for the temperature control means 102. The temperature control means 102 receives a current temperature PVm as a detection temperature detected by the thermocouple 105 which is provided in a vicinity of the heater. Then, the temperature control means 102 outputs a control output MVm obtained by PID arithmetic operation performed based on the target temperature SPm and the current temperature PVm. The distributor 103 temporarily stores the control output MVm. Thereafter, the distributor 103 supplies the control output MVm to each of the heater power sources 104M, 104S1, and 104S2 of the respective heaters.
The heater power source M for the main heater M receives, from the distributor 103, an output value Mvm of the temperature control means 102. The heater power sources S1 and S2 for the respective sub heaters S1 and S2 receive respective output values MVs1 and MVs2. The output values MVs1 and MVs2 are obtained based on the respective following equations (1) and (2) by multiplying the output value MVm of the temperature control means 102 by respective constant ratios αs1 and αs2 in the distributor 103.MVs1=MVm×αs1  (1)MVs2=MVm×αs2  (2)
In this case, if each of the heater power sources 104S1 and 104S2 is a power source having an electric power control specification, electric power having the constant ratios (αs1 and αs2) with respect to electric power to be supplied to the main heater M is supplied to the respective sub heaters S1 and S2.